Go for an 80 watt. As long as it is on a T-stat, it will only turn on when needed. Better to have more than you need than not enough when you need it. I personally use a Pro Products PH-3 which is the 65 watt in my Pro-Line 48x23x14 and it works fine. I will probably up my next one for my AP T-10 cage to a PH-3C which is their 75 watt RHP so I definitely have enough power.